5 – New roofs VS slate roofs

Hello slate people

For me, installation is, at least, as much important as the roofing slate quality. You might have a superb slate, but if the installation is not performed by a certified roofing contractor with experience in slate roofing (in other words, a good professional), things may go wrong. Choosing the correct installation system is critical. Nowadays, new technologies have been applied to roofing slate installation. For example, Newmont Slate Inc. has develop the Slate Shield, which allows to lighten the weight of a slate roof without losing performance. Other companies have patented a prefabricated system that takes advantage of the sun power to heat domestic water. These advances are very interesting, since they open the field of potential uses for roofing slate. But, what about the old installation system, the traditional ones? Are these systems obsolete? It is justified changing an old slate cover by a new one, made with a marvelous new covering material?

A paper published in 2011 might give some light to these questions. Sara Fasana and Riccardo Neva, researchers of the Department of Building Engineering of the Polytechnic School of Turin, wrote a review on how traditional roofing slate installation methods in Italy would be affected by wind. As you know, wind is a major player when designing a roof. Wind may not only force water to get under the roof but in certain cases it may even dismantle the cover. In areas with hurricanes, such as Florida, this is something to be very aware of. These researchers took into account several parameters, like pitch, design of the covering elements (tiles), attach system, etc., and submitted experimental roofs to several wind driven rain tests. What they found might not be a surprise for you. Old slate covers and styles are safe, since are the result of centuries of experience. Changing one of these old roofs by new trendy materials is not justified from a technical point of view:

“If the stone roofs in discussion were built with proper technical skills, they would be as water resistant as the ones built with different materials; so the common practice of substituting the stone roofs with roofs made of other materials is completely unjustified. At the same time, the recovery of building techniques and traditional laying are a way to preserve the technical material culture, which otherwise would be irremediably lost.”

Any question after this?

Have fun!

Image: Water infiltration depends not just on the wind force but on the shape of the edges. In A we can see how the water can come in when the edges are straight, while in B the shape of the edges prevents water to penetrate on the cover. Images taken from Fasana et al. 2011.

 

To know more:
Fasana, S., Nelva, R., 2011. Improvement of the performance of traditional stone roofs by wind driven rain experimental tests. Construction and Building Materials 25, 1491-1502.

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